The invention generally relates to aseptic double seat valves. More specifically the invention relates to aseptic double seat valves of the type comprising a housing, which has connections for two pipe conduits, a first valve seat and a second valve seat, wherein the valve seats are arranged spaced apart from one another in the direction of a longitudinal axis in the housing, between the connections for the two pipe conduits, a first closing body, which interacts in a sealing manner with the first valve seat, and a second closing body, which interacts in a sealing manner with the second valve seat, a first elongate valve stem, which is of hollow design and is connected to the first closing body, and a second elongate valve stem, which extends through the interior of the first valve stem and is connected to the second closing body, and a diaphragm, which has a radially inner opening and serves to seal off a gap present between the first valve stem and the second valve stem.
An aseptic double seat valve of the type stated above is used, in particular, in a process engineering plant in which aseptic working conditions are required. This applies especially to process engineering plants in the food industry, in the beverage industry and in the pharmaceutical industry.
As compared with a double seat valve which does not have to comply with aseptic conditions, there is a requirement in the case of an aseptic double seat valve that medium which flows through the housing of the double seat valve cannot penetrate into the gap between the inner, second valve stem and the hollow outer, first valve stem. For this purpose, the aseptic double seat valve as known from DE 10 2006 025 653 C5 has a diaphragm having a radially inner opening for sealing the gap present between the first valve stem and the second valve stem. In the case of the known aseptic double seat valve, the outer rim of the seal is fixed in a sealing manner on the closing body which is at the top in the installed position of the double seat valve, while the inner rim of the seal is fixed in a sealing manner on the inner valve stem, more specifically at a distance from the closing body which is at the bottom in the installed position of the double seat valve, which body is connected to the inner valve rod.
This construction of the known aseptic double seat valve leads to the following disadvantages. One disadvantage is that the known double seat valve is not easy to maintain and service because it does not allow a construction in which the diaphragm is part of a preassembled module. The diaphragm can be removed from the double seat valve only as a single part. If the diaphragm has to be exchanged, the double seat valve must be disassembled into many individual parts in the region of the closing bodies in order to be able to remove the diaphragm. Conversely, when installing a new diaphragm in the known double seat valve, it is not possible to preinstall the diaphragm on a module consisting of elements outside the valve housing and then to insert this module as a whole into the housing with the diaphragm already fixed on the module. It is therefore also not possible to replace functional subassemblies of the double seat valve with functionally identical but structurally different subassemblies. For example, it may be desirable to operate the double seat valve with some sealing system other than a diaphragm as a seal for sealing off the gap between the first and the second valve stem, e.g. a corrugated bellows. For this purpose, the known double seat valve would have to be completely rebuilt.
Another disadvantage of the known aseptic double seat valve is that of leakage monitoring. Particularly in the case of aseptic double seat valves, it is necessary during the operation of the double seat valve to continuously monitor whether the sealing element or elements present on the first closing body and on the second closing body are interacting in a sealing manner with the respective valve seat or whether there is leakage and hence transfer of medium past the corresponding sealing element into the leakage space. For this purpose, the aseptic double seat valve is connected to a leakage monitoring device.
In the known double seat valve, a leakage monitoring means is not provided at the closing body at the bottom in the installed position for the sealing element present thereon. As a result, the leakage space between the two closing bodies cannot be cleaned chemically but only by means of steam sterilisation. In the case of chemical cleaning, chemical cleaning agent could cross from the leakage space into the other pipe conduit if the sealing element of the lower closing body were not leaktight, and it would not be possible to detect this in the known double seat valve in the absence of leakage monitoring for the lower closing body. If the intention were to provide leakage monitoring at the lower closing body, the inner valve rod would have to be of hollow design or to be bored out in order to allow leakage monitoring through the inner valve rod. However, this would result in weakening of the inner valve rod.
Document WO 98/54493 A1 has furthermore disclosed an aseptic double seat valve which has a diaphragm that is fixed in a sealing manner on both closing bodies and which simultaneously has the sealing function for sealing off the closing bodies with respect to the valve seats.